One alleged incident cited involved a claim Ms Martens held the boy's head in a sink, allowing water to pour into his mouth, after the boy had splashed her during a family outing.

The allegations were flatly denied by Ms Martens. However, she lost her bid to become guardian of the children after her husband's killing last August, with it instead being granted to Mrs Lynch and her husband David in Limerick.

Court filings also reveal Ms Martens has signalled her intention to mount a fresh bid for custody. She filed a notice of appeal with North Carolina's Court of Appeals last month.

The move came after an initial appeal failed on December 8. It shows her intention to take fresh legal steps to gain custody of the children, who are now living with the Lynches in Ireland.

Earlier this week, Ms Martens and her father, former FBI agent Thomas Martens (65), were charged with the second-degree murder and voluntary manslaughter of Mr Corbett.

The Limerick man died from head injuries at the home he shared with Ms Martens in Wallburg, North Carolina, on August 2 last.

A police report said her father told a 911 dispatcher he had struck his son-in-law with a baseball bat during a row.

Ms Martens and her father claim they acted in self-defence and are out on bail.

However, the claims made against her during the custody battle are now likely to be revisited when their trial gets underway later this year or early in 2017.

Mr Corbett's first wife, Mags, died from an asthma attack in 2006. He subsequently hired Ms Martens as an au pair, but they later became romantically involved and married in her native Tennessee in 2011.

The family moved from Ireland to North Carolina, where Mr Corbett worked for a pharmaceutical company.

Disclosures indicating significant discord in their marriage are also likely to form a major plank of the murder case.

During the guardianship battle, it emerged Ms Martens had confided to a family friend in June or July 2013 that she had sought legal advice regarding custody of the children in the event of a divorce.

In the autumn of 2014, she also spoke to an attorney about her rights to the children.

Other findings of fact published by the Davidson County Superior Court were that Mr Corbett refused to consent to his wife adopting the children, after she had expressed a desire for a step-parent adoption.